A circuit implemented as a System-on-Chip (SOC) circuit comprising a microcontroller configured to drive one or more hard macros via a respective communication interface and a shielded bus. The microcontroller configured to transmit over the shielded bus random numbers to the hard macro. The microcontroller and the hard macro configured to use these random numbers as cryptographic shared secret for authentication. The microcontroller configured to drive via the communication interface the hard macros authenticated via the random numbers.